package com.ywj.collection.MyMap;

import java.util.HashMap;
import java.util.Map;

public class MapNull {
    public static void main(String[] args) {
        Map<Object, Object> map1 = new HashMap<>();
        map1.put("name", "wj");
        map1.put("study", null);
        map1.put(null, "unknown");
        map1.put(null, null);
        System.out.println(map1);
    }
}
